Swiss bank UBS said it had received subpoenas from U.S. and Japanese regulators regarding whether it made “improper attempts” to manipulate LIBOR rates, the benchmark price for interbank borrowing costs.

“UBS understands that the investigations focus on whether there were improper attempts by UBS, either acting on its own or together with others, to manipulate LIBOR rates at certain times,” the bank said in its annual report Tuesday.

UBS said it had received subpoenas from the  Securities and Exchange Commission, Commodity Futures Trading Commission and Department of Justice regarding its submissions to the British Bankers’ Association, which sets LIBOR rates.

It has also been ordered to provide information to the Japan Financial Supervisory Agency concerning similar matters.

UBS said it was conducting an internal review and is cooperating with the investigations. It declined to provide any further details. The SEC declined to comment.

BBA said LIBOR has a straightforward and transparent calculation method that excludes rates that are significant outliers.

“We observe rigorous standards in our scrutiny and governance of the LIBOR mechanism and work with the industry to ensure their continued full confidence in one of its most accurate and reliable benchmarks,”it said in a statement.

LIBOR is calculated daily by asking contributing banks the rate at which they expect term funding to be offered between prime banks at 1100 GMT. A set number of the highest and lowest contributions are discarded and the remaining rates averaged.